'93 F-150 5.0 engine Dual Tanks

Ok, so before I start I need to tell everyone that my fuel pump went on the front tank several years ago, Twice. Thinking that the tank was bad and rusted clogging the fuel pump I decided to punch the tank and drain the fuel so I didn't have to carry around all the weight of the full fuel tank......that was several years ago.

Jump to several weeks ago...... I notice (kinda hard not to when your lightheaded) there is raw fuel dripping out of the front tank (where I punched it). It's not constant and I have not noticed a dip in fuel millage, but it's really a nuance and a very dangerous situation.

I looked up in Haynes that there is a FDM (fuel delivery module) that sends the unused fuel back to the tank it came from. If this "FDM" senses that the tank is full it will send the unused fuel back to the other tank (in this case the punched front tank, hence the dripping). The manual says that this Module (FDM) is like a shutter and may stick open and not operated correctly (section 4-12).

OK now the million dollar question........
instead of pulling the rear fuel pump (which currently works) I was planning on just replacing the front tank and pump this way I will have a back up fuel pump and tank for when the rear one (eventually) dies.

Does this all sound correct?

thanks
L

 

Yes that sounds good, but I have to correct one thing there is no sensor in the FDM to switch tanks and fuel should never transfer from one to the other.. you have the common fuel transfer problem resulting from faulty/dirty check valves. Replacing the FDM in the front tank should cure this issue and improve your apparent fuel milage.

 

OH .....ok cool, I read it quickly and I'm not a professional mechanic, just a weekend warrior. so where are the check valves located.....(should I assume the check valve is on the fuel pump itself hence the backing up of fuel into the non-working (and check valve broken) front tank from the non-working (and check valve broken) fuel pump.

So when I replace the front tank fuel pump everything will b back to normal?

Thanks Paul

 

The check valves are inside the plastic FDM body and are not servicable as far as I know.. so if you buy a new FDM you get new check valves. There are several other threads on here about terrible gas milage and one of them has pics of a dismantled FDM with the parts labeled, have a quick look for it.

 

Ok, Thanks.......So Paul, when I replace the fuel pump do I have a separate FDM in the tank that needs to be replaced or is the word "FDM" just a fancy word for "fuel pump".

thanks for the help!!!

 

The FDM(fuel delivery module) is a plastic resovoir that contains the check valves and the pump itself, you need the whole thing since your check valves are causing problems and the pump doesn't work.